In the bowl of a stand mixer fitted with a paddle attachment, mix butter and sugar on medium speed for about 2 minutes. Add in egg yolks and beat until combined, followed by vanilla extract.

In another bowl, combine flour, cocoa powder and salt. Scrape down the sides of the mixing bowl, then slowly add in flour on low speed, mixing just until combined.

On a floured work surface, pat dough into a disc and cover with plastic wrap. Refrigerate for at least 1 hour, or up to 2 days.

Preheat oven to 350°F / 175°C. Line 2 baking sheets with parchment paper. Set aside.

On a lightly floured surface roll out dough into a ¼ inch thickness. Cut out cookies with a cookie cutter of your choice, using a smaller cookie cutter or piping tip to make a hole in the center of half of the cookies. Carefully place on the prepared baking sheets with about 1-2 inch space in-between.

Remaining dough can be rolled out again.

Bake each sheet for 12-15 minutes, just until bottoms lightly brown. Allow cooling on the baking sheet for 5 minutes then transfer to a cooling rack to cool completely. Sift confectioner's sugar on the cookies with holes in them.

Fill cooled cookies with chocolate hazelnut spread and sandwich together. 

Store in an airtight container at room temperature up to 3 days.